Electronic modules such as a voltage converter, a power amplifier, a monitor or the like exist in various electronic apparatus, such as tablet computers, smart phones, music players etc., and each electronic module has a rated current. When the current flowing in the electronic module exceeds the rated current, the electronic module will be burned out and cannot work. Therefore, it is necessary to set an overcurrent protection device in the electronic module so as to protect the entire electronic module when the current flowing through it is too large.
The various electronic modules require a power source to supply power so that they can work. Conventional overcurrent protection devices can achieve overcurrent protection by disconnecting the electronic module from the power source. However, cutting off the power supply of the electronic module may cause disturbance of its operation, and it is difficult to restart the operation of the electronic module, which may affect operations of other modules or electronic circuits associated with the electronic module.
Moreover, in the conventional overcurrent protection devices, overcurrent protection can also be achieved by controlling an internal current of the electronics module. However, it is difficult to effectively perform overcurrent protection in some cases. Discussion is provided below with the electronic module being a boost converter as example.
The boost converter serves for converting a specific DC input voltage Vin to a larger output voltage Vout so as to supply power to a function module in the electronic apparatus. In the operation process of the boost converter, the input electricity is temporarily stored in an electricity storage element such as an inductor, a capacitor and others (i.e., performing a charging process), and then the electricity is released at an output terminal with different voltages (i.e., performing a discharging process so that the input voltage Vin is converted to the desired output voltage Vout. The boost converter includes a control element such as a switch, and the control element is driven by a driving signal to control the charging and discharging process. When the current in the boost converter is too large, the overcurrent protection device drives the control element to only discharge, not charge, so as to expect a gradual decrease in the current of the storage device in the discharge process.
The overcurrent protection device in the above boost converter can protect the voltage converter well when the output voltage Vout is significantly greater than the input voltage Vin. However, when the output voltage Vout is close to the input voltage Vin, or when the load driven by the boost converter is too heavy and the output voltage Vout is caused to be lower than the input voltage Vin, the current reduction amount on the electricity storage element will be very small, even negative, i.e., it shows as a current increase on the electricity storage element. This can be seen from the following Equation (1)
                              Δ          ⁢                                          ⁢                      I            LD                          =                                            -                                                                    V                    ⁢                                                                                  ⁢                    out                                    -                                      V                    ⁢                                                                                  ⁢                    in                                                  L                                      ·            T                    ⁢                                          ⁢          off                                    Equation        ⁢                                  ⁢                  (          1          )                    where ΔILD is a current reduction amount on the electricity storage element, Vout is an output voltage of the boost converter, Vin is an input voltage of the boost converter, L is an inductance value of an inductor that serves as the electricity storage element, and Toff is a turn-off time during which the control element controls the electricity storage element to discharge. It can be known from to Equation (1) that, when the output voltage Vout is close to the input voltage Vin, the current decrease on the electricity storage element current is very small; when the output voltage Vout is lower than the input voltage Vin, the current decrease on the storage device is negative. Therefore, even if the overcurrent protection device detects that the current in the boost converter is too large and turns off the control element to control the current in the boost converter, it is still hard to effectively reduce the current therein so as to perform overcurrent protection on the boost converter. Here, failure of the overcurrent protection device is described with the overcurrent protection device in the boost converter as an example, there are similar problems in electronic modules having a power input such as an amplifier, a monitor etc.